The present invention relates to a fluid coupling union such as a fluid coolant rotating union having a secondary sealing assembly which provides a depressurized condition displacement of the floating seal members from one another to provide a pop-off or gap between the seal members when the cooling union is depressurized.
Fluid coolant unions are used extensively in conjunction with machine tools in various high speed drilling and boring transfer operations, high speed machine tool spindles, and in various applications such as machining centers and flexible transfer lines. In such applications, the rotating union is structurally arranged to conduct various types of coolants, such as water-based, oil-based, and air-based fluids into the machine tool spindle. Preferably, such coolants may be used without prolonged dry-run periods of operation of the coolant union. Coolant unions generally include conventional seal assemblies having a rotating seal member mounted to the end of the rotating rotor member, which seal member is axially aligned to engage a non-rotating complementary seal member which is mounted to an axially movable carrier member mounted within the housing.
In existing prior art coolant union assemblies, when the union is operating in the pressurized condition the sealing surface of the non-rotating seal member is biased into engagement with the sealing surface of the rotating seal member by overcoming some type of spring or baffle diaphragm bias means which is designed to axially separate the seal members when in the non-pressurized dry-running condition. As the liquid or fluid coolant is passed through the coolant union, the coolant lubricates the contacting seal members to minimize wear between the members. When the condition is reached where the union is unpressurized and fluid coolant is not passing through the union, a “dry running” condition is achieved and the facing surfaces of the rotating and non-rotating seal members do not receive any lubrication. During this dry-running condition, the increased wear on the seal facings results in leakage about the seal facings which ultimately require replacement of one or both of the seal members. Such replacement of the seal facing and the rotor assembly are expensive and time consuming.
To overcome the problems associated with dry-running, coolant unions have been developed to include structure which separates the rotating and non-rotating seal facings from one another when fluid coolant is not passing through the union. Such “pop-off” type unions may be biased by spring or diaphragm members. Such biasing members position the seal members apart from one another in the absence of the passage of fluid coolant passing through the union. However, such coolant unions are complex and expensive to manufacture. Also, during start-up of such coolant unions, excessive amounts of the fluid coolant are permitted to pass through the enlarged gap separating the rotating and non-rotating seal facings.